Full Engine Tune-Up

This procedure covers a complete tune-up service for the 5.9L Cummins diesel engine, including fuel filter replacement, air filter service, valve lash adjustment, and fuel system inspection.

Warnings

Tools required

Parts

• Fuel filter assembly with water separator × 1 — Mopar 68157291AA or equivalent
• Engine air filter × 1 — Use OEM specification
• Crankcase breather filter × 1 — Use OEM specification
• Valve cover gasket × 1 — Use OEM specification if reusing valve cover
• Drive belt(s) × 1 — Inspect and replace if worn

Fluids

• 15W-40 diesel engine oil or 5W-40 synthetic — 12 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely (minimum 2 hours after operation)
3. Disconnect both negative and positive battery cables to prevent accidental starter engagement during valve adjustment
4. Gather all tools, parts, and fluids before beginning work
5. Place drain pan under fuel filter housing area
6. Clean exterior of valve cover, fuel filter housing, and air filter housing to prevent contamination

Procedure

1. 1

   Replace engine air filter and crankcase breather
   Open the air filter housing by releasing the spring clips on the top cover. Remove the old air filter element and inspect the housing for debris or dirt accumulation. Clean the housing interior with a damp rag if needed. Install the new air filter element, ensuring proper seating in the housing. Locate the crankcase breather filter on the driver side valve cover and remove the retaining clip. Pull out the old breather filter and install the new one, ensuring it seats fully. Reinstall the retaining clip and close the air filter housing. Verify the correct Mopar fuel filter/water separator part number for your specific 2007 5.9L Cummins against manufacturer documentation before ordering.
2. 2

   Drain fuel filter water separator
   Locate the fuel filter/water separator assembly on the driver side of the engine block. Place a drain pan underneath the filter housing. Open the water drain valve at the bottom of the fuel filter housing by turning it counterclockwise. Allow any accumulated water and sediment to drain completely (typically 1-2 cups maximum). Close the drain valve by turning it clockwise until snug. Do not overtighten the plastic drain valve.
3. 3

   Replace fuel filter assembly
   Use a fuel filter wrench or large strap wrench to loosen the fuel filter canister by turning counterclockwise. Be prepared for fuel spillage into the drain pan. Once loose, unscrew the filter by hand and allow it to drain completely. Clean the filter head mounting surface with a clean rag. Inspect the filter head O-ring sealing surface for damage. Fill the new fuel filter approximately 2/3 full with clean diesel fuel to aid in priming. Lubricate the O-ring seal on the new filter with clean diesel fuel. Thread the new filter onto the filter head by hand, turning clockwise. Once the O-ring contacts the filter head, tighten an additional 1/2 to 3/4 turn by hand only. Do not use a wrench to tighten.
4. 4

   Prime fuel system
   Locate the primer pump on top of the fuel filter housing. Operate the primer pump (lift-and-press motion) until firm resistance is felt, indicating the fuel system is primed. This typically requires 50-100 strokes. Check the fuel filter base and drain valve for any fuel leaks. Wipe away any spilled fuel. Reconnect the battery cables temporarily and turn the ignition key to the RUN position without starting the engine to activate the electric lift pump for 30 seconds. Repeat 2-3 times to fully prime the system. Check again for leaks.
5. 5

   Remove valve cover
   Disconnect battery cables again before proceeding. Disconnect any electrical connectors attached to the valve cover (typically the crankcase pressure sensor). Remove the fuel lines or brackets that may obstruct valve cover removal, noting their positions for reinstallation. Remove the valve cover bolts in a crisscross pattern to prevent warping. Note the exact number of valve cover bolts as you remove them (verify count against the service manual) and remove them in a crisscross pattern. Carefully lift the valve cover away from the cylinder head. If the gasket is stuck, gently tap the cover with a rubber mallet to break the seal. Do not pry between the cover and head with a screwdriver as this can damage the sealing surfaces.
   Torque spec

   Valve Cover Bolts10 Nm (7 lb-ft)
6. 6

   Inspect valve train components
   With the valve cover removed, visually inspect all rocker arms, pushrods, and valve springs for damage, excessive wear, or unusual patterns. Check for loose or damaged rocker arm adjusting screws. Inspect the valve cover gasket and replace if damaged, brittle, or compressed. Clean any oil sludge or debris from the valve cover interior and cylinder head surface using shop rags. Verify that all pushrods are straight by rolling them on a flat surface.
7. 7

   Rotate engine to TDC cylinder 1
   Using a 15/16-inch socket on the crankshaft pulley bolt, rotate the engine clockwise (viewed from front) until the timing mark on the crankshaft pulley aligns with the TDC indicator on the timing cover. Verify cylinder 1 is at TDC compression stroke by confirming both intake and exhaust valves for cylinder 1 are closed (rocker arms should have clearance and move freely). If valves are not closed, rotate the engine one complete additional revolution (360 degrees) to TDC. The firing order is 1-5-3-6-2-4. Cylinders are numbered from front to rear.
8. 8

   Adjust valve lash on first group
   With cylinder 1 at TDC compression stroke, adjust valves on cylinders 1, 2, and 3 (both intake and exhaust for each). The valve lash specification on a cold engine is 0.010 inches (0.254mm) for intake valves and 0.020 inches (0.508mm) for exhaust valves. Verify against the current Cummins service manual for your specific engine. To adjust: loosen the rocker arm adjusting screw locknut while holding the adjusting screw steady. Insert the 0.010-inch feeler gauge between the rocker arm and valve crosshead (the bridge above the two valves). Turn the adjusting screw until there is a slight drag on the feeler gauge - it should pull through with moderate resistance but not be loose or too tight. Hold the adjusting screw and tighten the locknut to the manufacturer-specified torque (verify in the Cummins service manual; commonly approximately 18 ft-lbs / 24 Nm). Recheck the clearance after tightening. Repeat for all valves in cylinders 1, 2, and 3.
9. 9

   Adjust valve lash on second group
   Rotate the crankshaft clockwise exactly 360 degrees (one full revolution) to bring cylinder 6 to TDC compression stroke. Verify cylinder 6 valves are both closed. With cylinder 6 at TDC compression stroke, adjust valves on cylinders 4, 5, and 6 using intake spec 0.010 inches and exhaust spec 0.020 inches, following the same procedure as in the previous step. Use the appropriate feeler gauge for each valve type. After completing all valve adjustments, double-check several random valves to verify proper lash and locknut tightness.
10. 10

    Reinstall valve cover
    Clean both the valve cover and cylinder head gasket mating surfaces thoroughly with a clean rag. Ensure no oil or debris is present. If installing a new gasket, remove the old gasket completely and clean any residual gasket material. Position the new or reusable gasket on the cylinder head, aligning all bolt holes. Some gaskets have locating tabs or adhesive backing. Carefully position the valve cover onto the cylinder head, ensuring the gasket remains properly seated. Install the valve cover bolts finger-tight first. Tighten them in a crisscross pattern from the center outward to the manufacturer-specified torque (commonly approximately 18 ft-lbs / 24 Nm — verify in the service manual). This prevents gasket distortion and ensures even clamping pressure.
    Torque spec

    Valve Cover Bolts10 Nm (7 lb-ft)
11. 11

    Inspect and adjust drive belt(s)
    Visually inspect the serpentine drive belt for cracks, glazing, fraying, or chunks missing from the ribs. Check belt tension by pressing on the belt midway between pulleys - deflection should be approximately 1/2 inch with moderate thumb pressure. If the belt shows wear or tension is incorrect, replace or adjust the belt using the automatic tensioner or adjustable idler pulley. On the 5.9L Cummins, the belt tensioner is spring-loaded and automatic. If tension is insufficient, the tensioner may need replacement. Ensure the belt is properly seated in all pulley grooves.
12. 12

    Reconnect components and check fluid levels
    Reconnect all fuel lines, brackets, and electrical connectors that were removed from the valve cover area. Ensure all connections are secure and properly routed. Reconnect the battery cables (positive first, then negative). Check the engine oil level on the dipstick and add oil if necessary to bring it to the full mark. The 5.9L Cummins holds approximately 11-12 quarts with filter; verify the exact capacity in the owner's manual and fill to the dipstick full mark. Check coolant level in the overflow reservoir and top off if needed with 50/50 HOAT coolant mixture.

Reassembly

1. Verify all valve cover bolts are torqued to specification in proper sequence
2. Ensure all electrical connectors and fuel lines are properly reconnected
3. Confirm no tools or rags are left in the engine compartment
4. Verify air filter housing is properly sealed and all clips are engaged

Verification

• Start the engine and allow it to idle. Listen for unusual valve train noise - properly adjusted valves should operate quietly without excessive ticking or clattering
• Check for fuel leaks around the fuel filter housing and drain valve while engine is running
• Check for oil leaks around the valve cover gasket perimeter
• Verify smooth idle quality and normal engine operation. The engine should start easily after priming
• Monitor the fuel filter water separator indicator (if equipped) to verify proper fuel flow
• Test drive the vehicle to verify normal power delivery and ensure no warning lights are illuminated
• After test drive, recheck valve cover area for oil leaks and fuel filter for fuel leaks
• Schedule next valve lash adjustment according to maintenance schedule (typically every 100,000 miles or as needed based on valve train noise)

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